Re: [css-compositing] "add" and "subtract" blend modes

On Thu, Aug 23, 2012 at 11:03 AM, Tab Atkins Jr. <jackalmage@gmail.com>wrote:

> On Thu, Aug 23, 2012 at 10:55 AM, Rik Cabanier <cabanier@gmail.com> wrote:
> > thanks for your feedback!
> > Do you feel strongly that these blend modes should be in the first
> > specification, or do you think they could wait until the next version?
> > Looking at the open source browsers, there is no support under the hood
> for
> > these Photoshop specific blend modes which might slow down
> implementation.
>
> I may be off-base, but the cross-fade() function in Images 4
> <http://dev.w3.org/csswg/css4-images/#cross-fade-function> uses the
> 'add' PD operator.  Is that the same as the linear-dodge blend mode?
> If so, then we have an implementation of it in WebKit.
>
>
That is the 'lighter' compositing mode [1] which adds all the values
(including alpha) of the source and destination.
'Linear dodge' adds the color components and then applies the blending
stages [2]. This will give a more pleasing result.

Rik

1:
https://dvcs.w3.org/hg/FXTF/rawfile/tip/compositing/index.html#porterduffcompositingoperators_plus

2: https://dvcs.w3.org/hg/FXTF/rawfile/tip/compositing/index.html#blending